/Engine/Plugins/Experimental/GeometryScripting/Source/GeometryScriptingCore/Public/GeometryScript/ShapeFunctions.h
Get the position of a corner of the Box. Corners are indexed from 0 to 7, using an ordering where 0 is the Min corner, 1/2/3 are +Z/+Y/+X from the Min corner, 7 is the Max corner, and 4/5/6 are -Z/-Y/-X from the Max corner.
static FVector GetBoxCorner ( FBox Box, int CornerIndex )